Field of the Invention
Embodiments of the invention relate generally to the field of computer systems. More particularly, embodiments of the invention relate to the improvement of the responsiveness of sleep state transitions using non-volatile random access memory.
Description of the Related Art
A. Current Memory and Storage Configurations
One of the limiting factors for computer innovation today is memory and storage technology. In conventional computer systems, system memory (also known as main memory, primary memory, executable memory) is typically implemented by dynamic random access memory (DRAM). DRAM-based memory consumes power even when no memory reads or writes occur because it constantly recharges internal capacitors. DRAM-based memory is volatile, which means data stored in DRAM memory is lost once the power is removed.
For many computer systems, especially mobile platforms, power utilization is a critical issue in terms of cost and performance. Generally, users have higher expectations on modern platforms with respect to immediate user-perceived responses to ON transitions, application starts, etc., in addition to a long-lasting battery life. To implement instant responsiveness, these platforms keep application state active in fast volatile DRAM, while maintaining the power on the DRAM even when the system is unused. DRAM power is a significant drain on battery life. Thus, many conventional platforms have to reduce the memory capacity in order to prolong its battery life.
B. Phase-Change Memory (PCM) and Related Technologies
Phase-change memory (PCM), also sometimes referred to as phase change random access memory (PRAM or PCRAM), PCME, Ovonic Unified Memory, or Chalcogenide RAM (C-RAM), is a type of non-volatile computer memory which exploits the unique behavior of chalcogenide glass. As a result of heat produced by the passage of an electric current, chalcogenide glass can be switched between two states: crystalline and amorphous. Recent versions of PCM can achieve two additional distinct states, effectively doubling memory storage capacity.
PCM provides higher performance than flash because the memory element of PCM can be switched more quickly, writing (changing individual bits to either 1 or 0) can be done without the need to first erase an entire block of cells, and degradation from writes is slower (a PCM device may survive approximately 100 million write cycles; PCM degradation is due to thermal expansion during programming, metal (and other material) migration, and other mechanisms).